In 1935, Robert Bloch wrote to H. P. Lovecraft and politely asked permission to murder him. Lovecraft said "Yes."
One of Lovecraft's traits was that he wrote to, visited, and mentored many other authors. In some cases, established writers such as Robert E. Howard (Conan); even with Howard you can see tales in which he used Lovecraft's advice to good effect.
In other cases, Lovecraft helped novice writers polish and improve theirs skills. He encouraged them to use his own creations in his tales, so Lovecraft basically invented the "shared universe" idea. One of the young authors he helped on his way was Robert Bloch who at age 16 started corresponding with Lovecraft. Later, Bloch wrote a number of terrific horror books and stories, famously including Psycho. (My favorite story by Bloch is The Screaming People. Check it out.)
Bloch also wrote Lovecraft-style horror stories (he returned to Lovecraft in 1978 with Strange Eons). When Bloch was 18, he asked Lovecraft in a letter if he could kill him off in a story he'd thought up. Lovecraft responded with a certificate giving Bloch the authority to maim, disintegrate, transmogrify, annihilate, etc. Lovecraft however he saw fit. Lovecraft then added the signatures of Yog-Sothoth, Cthulhu, and other Great Old Ones and Outer Gods formally granting Bloch permission. Bloch, naturally, kept this certificate as a treasure. (As a side note can I just say that Lovecraft's anti-semitism was non-existent - he married a Jewish woman. He liked and mentored Robert Bloch, who was Jewish. And so forth.)
So Bloch wrote the tale "The Shambler From the Stars" which is a parody of Lovecraft's own style. The parody is pretty subtle and never overtly stilly, but it does include things such as "I yearned to know the kiss of the worm upon my tongue" which even Lovecraft wouldn't have written. Anyway, the hero goes to visit an unnamed "Providence Dreamer" who is REALLY OBVIOUSLY Lovecraft, and shows him this weird book "De Vermiis Mysteriis" (which is where the book came from if you recognize it from my game stuff). Lovecraft then immediately reads a spell out of the book and a monster comes and eats him. The End. This story is also the source of the monster I named the Star Vampire in my books. Now you know.
It wasn't over though. Because Lovecraft responded with a story "The Haunter of the Dark" in which a character named "Robert Blake" - obviously Robert Bloch - finds out Too Much about the abandoned Starry Wisdom church and gets in trouble with the Haunter of the Dark. And is of course horribly killed.
So Lovecraft & Bloch destroyed one another and we got THREE cool stories out of it. "Three?" you ask. Yes, three, because about a decade after Lovecraft died, Robert Bloch wrote The Shadow From the Steeple, which is a direct sequel to Lovecraft's The Haunter of the Dark.
Fun fact: we learn in Shadow from the Steeple that Nyarlathotep is behind the Manhattan Project. Makes sense, no?
Anyway it's a fun interaction between two great authors that I think is educational and superior to the idiotic and enervating feuds that we see all too frequently in writer's circles.
Are you familiar with Bloch's work? If not, at least have you read Lovecraft? Both authors wrote great short stories so you don't have to commit to a tedious 1200 page slog (unlike some authors). Check these guys out. In fact, make recommendations on other stories, or other authors that would be fun reads.